How Many Vehicles Can the RavTrack System Support

The number of vehicles that the RavTrack GPS tracking system can support depends upon the desired update rate, the over-the-air baud rate, and the number of repeaters. Because RavTrack PC interprets the ID as a decimal number, the maximum number of IDs when running RavTrack PC is 9999 vehicles. If you are using other software the limit may be different because the ID is a hexidecimal number, so there can be up to 65,000 unique IDs in your system.

100 vehicles with updates every 10 seconds, or 1000 vehicles with updates every 100 seconds. This is using 4800-baudover-the-air.

Narrow Band Channels

200 vehicles with updates every 10 seconds, or 2000 vehicles with updates every 100 seconds. This is using 9600-baudover-the-air.

The ID structure in the M7 GXmodem is 16-bits, allowing for over 65,000 unique IDs, and therefore 65,000 uniquely identified radios. But there are other practical limits to consider in a large system. How often are updates needed? How manyRF channels will be used? How many repeaters will be used?

In real-time tracking, each M7 GX uses some multiple of 50mS time slots (10mS in firmware C2 and higher) to report their positions. For 4800 baud, the M7 GX needs 100mS slots. If run at 9600 baud, it only needs 50mS to report position and status. A typical M7 GX at 4800-baud over-the-air rate uses 100mS to report its position.

If a repeater is used in the system, then it needs another 100mS torepeat the message, so the width of the time-slot allocated to each unit would be 200mS total. This number is programmable in the M7 GX; the factory default is 200mS.

Therefore, in one second, five M7 GX transponders could report, and have their messages repeated once.

In one minute, 300 transponders could report in. In 5 minutes, 1500. In one hour, 18,000. But only if each one reported once during thatinterval.

The formula for the number of possible M7 GX transponders in use at one time is:

N = S X R X U (seconds)
S = Slot time programmed into the M7 GX (0.10 for 4800 baud 0.005 for 9600 baud)
R = Number of repeaters that must sequentially repeat the transmission (Typical systems will have one repeater.)
U = Update Rate (This is the number of seconds between position reports.)

For systems up to about 300-500 units, this TDMA approach is veryefficient. If 1000’s of devices must be tracked, and there is only one RF channel available, the Update Rate in the M7 GX can be set to a small number, such as 10 seconds, but the report-by-exception features should be used. These stop the M7 GXfrom transmitting its data unless an exception occurs (input change,speeding, proximity alert, etc.). When exception reporting is used, theRF channel is not used unless an exception occurs. Typically the user will program the M7 GX to report once-per-hour or once-per-day even if an exception does not occur